arXiv subjects

Hua-Xing Chen

Publications and source records attributed to Hua-Xing Chen.

At least 145 records · Page 8Linked to original sources

arXiv2014

Thermodynamics of hadrons using the Gaussian functional method in the linear sigma model

We investigate thermodynamics of hadrons using the Gaussian functional method (GFM) at finite temperature. Since the interaction among mesons is very large, we take into account fluctuations of mesons around their mean field values using the GFM. We obtain the ground state energy by solving the Schrödinger equation. The meson masses are obtained using the energy minimization condition. The resulting mass of the Nambu-Goldstone boson is not zero even in the spontaneous chiral symmetry broken phase due to the non-perturbative effect. We consider then the bound state of mesons using the Bethe-Salpeter equation and show that the Nambu-Goldstone theorem is recovered. We investigate further the behavior of the meson masses and the mean filed value as functions of temperature for the cases of chiral limit and explicit chiral symmetry breaking.

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arXiv2013

How fast can an unstable particle decay into two final states and be observed

We investigate unstable hadrons (resonances) which mainly decay into two final states in a very short time. We estimate how far at most these two final states can travel away from each other in the half-life of the initial unstable hadron. As examples, this distance is about 2.5 fm for rho -> pi pi, 1.8 fm for Delta -> N pi, and 0.6 fm for f_0(500) -> pi pi. We calculate this distance for altogether 181 hadrons, among all the 324 ones listed in PDG2012 together with Zc(3900) and Zc(4025). We find it is around one femtometer for many hadrons, which is of the same order of magnitude as the hadronic radii. We also estimate this distance for altogether 15 unstable nuclei. We find it is about several femtometers for some of them, which is of the same order of magnitude as the nuclear radii. For example, it is about six femtometers for O12 -> N11 p.

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arXiv2013

Chiral Structure of Vector and Axial-Vector Tetraquark Currents

We investigate the chiral structure of local vector and axial-vector tetraquark currents, and study their chiral transformation properties. We consider the charge-conjugation parity and classify all the isovector vector and axial-vector local tetraquark currents of quantum numbers I(G)J(PC)=1(-)1(-+), I(G)J(PC)=1(+)1(--), I(G)J(PC)=1(-)1(++) and I(G)J(PC)=1(+)1(+-). We find that there is a one to one correspondence among them. Using these currents, we perform QCD sum rule analyses. Our results suggest that there is a missing b1 state having I(G)J(PC)=1(+)1(+-) and a mass around 1.47-1.66 GeV.

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arXiv2013

Chiral Structure of Scalar and Pseudoscalar Mesons

We systematically study the chiral structure of local tetraquark currents of flavor singlet and J(P)=0(+). We also investigate their chiral partners, including scalar and pseudoscalar tetraquark currents of flavor singlet, octet, 10, 10_bar and 27. We study their chiral transformation properties. Particularly, we use the tetraquark currents belonging to the "non-exotic" [(3_bar,3)+(3,3_bar)] chiral multiplets to calculate the masses of light scalar mesons through QCD sum rule. The two-point correlation functions are calculated including all terms and only the connected parts. The results are consistent with the experimental values.

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arXiv2013

Bi-Local Baryon Interpolating Fields with Three Flavours

Fierz identities follow from permutations of quark indices and thus determine which chiral multiplets of baryon fields are Pauli-allowed, and which are not. In a previous paper we have investigated the Fierz identities of baryon fields with two light flavours and found that all bilocal fields that can be constructed from three quarks are Pauli-allowed. That does not mean that all possible chiral multiplets exist, however: some chiral multiplets do not appear among structures with a given spin in the local limit, say J = 1/2. One such chiral multiplet is the [(6,3)+(3,6)], which is necessary for a successful chiral mixing phenomenology. In the present paper we extend those methods to three light flavors, i.e. to SU_F(3) symmetry and explicitly construct all three necessary chiral SU_L(3)*SU_R(3) multiplets, viz. [(6,3)+(3,6)], [(3,3_bar)+(3_bar,3)] and [(3_bar,3)+(3,3_bar)] that are necessary for a phenomenologically successful chiral mixing. We complete this analysis by considering some bi-local baryon fields that are sufficient for the construction of the "missing" spin 1/2 baryon interpolating fields. Bi-local baryon fields have definite total angular momentum only in the local limit. The physical significance of these results lies in the fact that they show that there is no need for higher Fock space components, such as the (q^4 q_bar), in the baryon chiral mixing framework, for the purpose of fitting the observed axial couplings and magnetic moments: all of the sufficient "mirror components" exist as bi-local fields.

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arXiv2013

The pion-pion Interaction in the rho Channel in Finite Volume

The aim of this paper is to investigate an efficient strategy that allows to obtain pi-pi phase shifts and rho meson properties from QCD lattice data with high precision. For this purpose we evaluate the levels of the pi-pi system in the rho channel in finite volume using chiral unitary theory. We investigate the dependence on the pi mass and compare with other approaches which use QCD lattice calculations and effective theories. We also illustrate the errors induced by using the conventional Luscher approach instead of a more accurate one recently developed that takes into account exactly the relativistic two meson propagators. Finally we make use of this latter approach to solve the inverse problem, getting pi-pi phase shifts from "synthetic" lattice data, providing an optimal strategy and showing which accuracy is needed in these data to obtain the $ρ$ properties with a desired accuracy.

hep-lat↗

arXiv2012

The "Closed" Chiral Symmetry and Its Application to Tetraquark

We investigate the chiral (flavor) structure of tetraquarks, and study chiral transformation properties of the "non-exotic" [(3_bar,3)+(3,3_bar)] and [(8,1)+(1,8)] tetraquark chiral multiplets. We find that as long as this kind of tetraquark states contains one quark and one antiquark having the same chirality, such as (q_L q_L \bar q_L \bar q_R + q_R q_R \bar q_R \bar q_L), they transform in the same way as the lowest level (\bar q q) chiral multiplets under chiral transformations. There is only one [(3_bar,3)+(3,3_bar)] chiral multiplet whose quark-antiquark pairs all have the opposite chirality (q_L q_L \bar q_R \bar q_R + q_R q_R \bar q_L \bar q_L), and it transforms differently from others. Based on these studies, we construct local tetraquark currents belonging to the "non-exotic" chiral multiplet [(3_bar,3)+(3,3_bar)] and having quantum numbers J^{PC}=1^{-+}.

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arXiv2012

Chiral Baryon Fields in the QCD Sum Rule

We study the structure of local baryon fields using the method of QCD sum rule. We only consider the single baryon fields and calculate their operator product expansions. We find that the octet baryon fields belonging to the chiral representations [(3,3*)+(3*,3)] and [(8,1)+(1,8)] and the decuplet baryon fields belonging to the chiral representations [(3,6)+(6,3)] lead to the baryon masses which are consistent with the experimental data of ground baryon masses. We also calculate their decay constants, check our normalizations for baryon fields in PRD81:054002(2010) and find that they are well-defined.

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arXiv2012

Baryon Tri-local Interpolating Fields

We systematically investigate tri-local (non-local) three-quark baryon fields with U_L(2)*U_R(2) chiral symmetry, according to their Lorentz and isospin (flavor) group representations. We note that they can also be called as "nucleon wave functions" due to this full non-locality. We study their chiral transformation properties and find all the possible chiral multiplets consisting J=1/2 and J=3/2 baryon fields. We find that the axial coupling constant |g_A| = 5/3 is only for nucleon fields belonging to the chiral representation (1/2,1)+(1,1/2) which contains both nucleon fields and Delta fields. Moreover, all the nucleon fields belonging to this representation have |g_A| = 5/3.

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arXiv2012

Baryons with U_L(3)*U_R(3) Chiral Symmetry IV: Interactions with Chiral (8,1)+(1,8) Vector and Axial-vector Mesons and Anomalous Magnetic Moments

We construct all SU_L(3)*SU_R(3) chirally invariant anomalous magnetic, i.e. involving a Pauli tensor and one-derivative, interactions of one chiral-[(8,1)+(1,8)] meson field with chiral-[(6,3)+(3,6)], [(3,\bar3)+(\bar3,3)], and [(8,1)+(1,8)] baryon fields and their "mirror" images. We find strong chiral selection rules: e.g. there is only one off-diagonal chirally symmetric anomalous magnetic interaction between J=1/2 fields belonging to the [(6,3)+(3,6)] and the [(3,\bar3)+(\bar3,3)] chiral multiplets. We also study the chiral selection rules for the anomalous magnetic interactions of the [(3,\bar3)+(\bar3,3)] and the [(8,1)+(1,8)] baryon fields. Again, no diagonal and only one off-diagonal chiral SU_L(3)*SU_R(3) interaction of this type is allowed, that turns out also to conserve the U_A(1) symmetry. We calculate the F/D ratios for the baryons' anomalous magnetic moments predicted by these interactions in the SU(3) symmetry limit and find that only the [(6,3)+(3,6)]-[(3,\bar3)+(\bar3,3)] one, reproduces F/D=1/3, in close proximity to the value extracted from experiment.

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arXiv2011

rho-rho-N and rho-rho-Delta molecules with $J^P=5/2^{+}$ and $J^P=7/2^{+}$

The rho-rho-N and rho-rho-Delta three-body systems have been studied within the framework of the fixed center approximation of Faddeev equation. The rho-rho interaction in isospin I=0, spin S=2 is strongly attractive, and so are the N-rho, Delta-rho interactions. This leads to bound states of both rho-rho-N and rho-rho-Delta. We find peaks of the modulus squared of the scattering matrix around 2227 MeV for rho-rho-N, and 2372 MeV for rho-rho-Delta. Yet, the strength of the peak for the rho-rho-N amplitude is much smaller than for rho-rho-Delta, weakening the case for a rho-rho-N bound state, or a dominant rho-rho-N component. A discussion is made on how these states can be searched for in present programs looking for multimeson final states in different reactions.

nucl-th↗

arXiv2011

The pp->p Lambda K+ and pp->p Sigma0 K+ reactions with chiral dynamics

We report on a theoretical study of the pp->p Lambda K+ and pp->p Sigma0 K+ reactions near threshold using a chiral dynamical approach. The production process is described by single-pion and single-kaon exchange. The final state interactions of nucleon-hyperon, K-hyperon and K-nucleon systems are also taken into account. We show that our model leads to a fair description of the experimental data on the total cross section of the pp->p Lambda K+ and pp->p Sigma0 K+ reactions. We find that the experimental observed strong suppression of Sigma0 production compared to Lambda production at the same excess energy can be explained. However, ignorance of phases between some amplitudes does not allow to properly account for the nucleon-hyperon final state interaction for the pp->p Sigma0 K+ reaction. We also demonstrate that the invariant mass distribution and the Dalitz plot provide direct information about the Lambda and Sigma0 production mechanism, and can be tested by experiments at COSY or HIRFL-CSR.

nucl-th↗

arXiv2011

The pp -> p Lambda K+ and pp -> p Sigma0 K+ Reactions in the Chiral Unitary Approach

We study the pp -> p Lambda K+ and pp -> p Sigma0 K+ reactions near threshold by using a chiral unitary approach. We consider the single-pion and single-kaon exchange as well as the final state interactions of nucleon-hyperon, K-hyperon and K-nucleon systems. Our results on the total cross section of the pp -> p Lambda K+ reaction is consistent with the experimental data, and the experimental observed strong suppression of Sigma0 production compared to Lambda production at the same excess energy can also be explained in our model.

nucl-th↗

arXiv2011

The Decay Properties of the 1^{-+} Hybrid State

Within the framework of the QCD sum rules, we consider the three-point correlation function, work at the limit q^2 -> 0 and m_π-> 0, and pick out the singular term ~ {1\over q^2} to extract the pionic coupling constants of the 1^{-+} hybrid meson. Then we calculate the decay widths of different modes. The decay width of the S-wave modes b_1 π, f_1πincreases quickly as the hybrid meson mass and decay momentum increase. But for the low mass hybrid meson around 1.6 GeV, the P-wave decay mode ρπis very important and its width is around 180 MeV, while the widths of ηπand η^\prime πare strongly suppressed. We suggest the experimental search of π_1(1600) through the decay chains at BESIII: e^+e^- -> J/ψ(ψ') -> π_1 +γor e^+e^- -> J/ψ(ψ') -> π_1 +ρwhere the π_1 state can be reconstructed through the decay modes π_1 -> ρπ-> π^+π^-π^0 or π_1 -> f_1(1285)π^0. It is also interesting to look for π_1 using the available BELLE/BABAR data through the process e^+e^- -> γ^\ast -> ρπ_1, b_1π_1, γπ_1 etc.

hep-ph↗

arXiv2011

Bi-local baryon interpolating fields with two flavours

We construct bi-local interpolating field operators for baryons consisting of three quarks with two flavors, assuming good isospin symmetry. We use the restrictions following from the Pauli principle to derive relations/identities among the baryon operators with identical quantum numbers. Such relations that follow from the combined spatial, Dirac, color, and isospin Fierz transformations may be called the (total/complete) Fierz identities. These relations reduce the number of independent baryon operators with any given spin and isospin. We also study the Abelian and non-Abelian chiral transformation properties of these fields and place them into baryon chiral multiplets. Thus we derive the independent baryon interpolating fields with given values of spin (Lorentz group representation), chiral symmetry ($U_L(2) \times U_R(2)$ group representation) and isospin appropriate for the first angular excited states of the nucleon.

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arXiv2010

Baryon Fields with U_L(3) times U_R(3) Chiral Symmetry III: Interactions with Chiral (3,3_bar)+(3_bar,3) Spinless Mesons

Three-quark nucleon interpolating fields in QCD have well-defined SU_L(3)*SU_R(3) and U_A(1) chiral transformation properties, viz. [(6,3)+(3,6)], [(3,3_bar)+(3_bar,3)], [(8,1)+(1,8)] and their "mirror" images, Ref.[9]. It has been shown (phenomenologically) in Ref.[3] that mixing of the [(6,3)+(3,6)] chiral multiplet with one ordinary ("naive") and one "mirror" field belonging to the [(3,3_bar)+(3_bar,3)], [(8,1)+(1,8)] multiplets can be used to fit the values of the isovector (g_A^3) and the flavor-singlet (isoscalar) axial coupling (g_A^0) of the nucleon and then predict the axial F and D coefficients, or vice versa, in reasonable agreement with experiment. In an attempt to derive such mixing from an effective Lagrangian, we construct all SU_L(3)*SU_R(3) chirally invariant non-derivative one-meson-baryon interactions and then calculate the mixing angles in terms of baryons' masses. It turns out that there are (strong) selection rules: for example, there is only one non-derivative chirally symmetric interaction between J=1/2 fields belonging to the [(6,3)+(3,6)] and the [(3,3_bar)+(3_bar,3)] chiral multiplets, that is also U_A(1) symmetric. We also study the chiral interactions of the [(3,3_bar)+(3_bar,3)] and [(8,1)+(1,8)] nucleon fields. Again, there are selection rules that allow only one off-diagonal non-derivative chiral SU_L(3)*SU_R(3) interaction of this type, that also explicitly breaks the U_A(1) symmetry. We use this interaction to calculate the corresponding mixing angles in terms of baryon masses and fit two lowest lying observed nucleon (resonance) masses, thus predicting the third (J=1/2, I=3/2) Delta resonance, as well as one or two flavor-singlet Lambda hyperon(s), depending on the type of mixing. The effective chiral Lagrangians derived here may be applied to high density matter calculations.

hep-ph↗

arXiv2010

The Strong Decay Patterns of the $1^{-+}$ Exotic Hybrid Mesons

We calculate the coupling constants of the decay modes $1^{-+}\rightarrowρπ, f_1π, b_1π, ηπ, η'π, a_1π, f_1η$ within the framework of the light-cone QCD sum rule. Then we calculate the partial width of these decay channels, which differ greatly from the existing calculations using phenomenological models. For the isovector $1^{-+}$ state, the dominant decay modes are $ρπ, f_1π$. For its isoscalar partner, its dominant decay mode is $a_1π$. We also discuss the possible search of the $1^{-+}$ state at BESIII, for example through the decay chains $J/ψ(ψ')\to π_1 +γ$ or $J/ψ(ψ')\to π_1 +ρ$ where $π_1$ can be reconstructed through the decay modes $π_1\to ρπ\to π^+π^-π^0$ or $π_1\to f_1(1285)π^0$. Hopefully the present work will be helpful to the experimental establishment of the $1^{-+}$ hybrid meson.

hep-ph↗

arXiv2010

Light Scalar Meson sigma(600) in QCD Sum Rule with Continuum

The light scalar meson sigma(600) is known to appear at low excitation energy with very large width on top of continuum states. We investigate it in the QCD sum rule as an example of resonance structures appearing above the corresponding thresholds. We use all the possible local tetraquark currents by taking linear combinations of five independent local ones. We ought to consider the pi-pi continuum contribution in the phenomenological side of the QCD sum rule in order to obtain a good sum rule signal. We study the stability of the extracted mass against the Borel mass and the threshold value and find the sigma(600) mass at 530 MeV +- 40 MeV. In addition we find the extracted mass has an increasing tendency with the Borel mass, which is interpreted as caused by the width of the resonance.

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